Jun.29 (GMM) Nico Rosberg is charging to maintain his fresh run of top form.

After winning in Austria, the German quickly returned to the wheel of the Mercedes in the post-race test at the same Red Bull Ring.

Derek Warwick, president of the Silverstone owner the British Racing Drivers' Club, told Sky he cannot understand why Lewis Hamilton did not push to do the test himself.

"He was off the pace all weekend in Austria, he had a bad start, I'd want to be trying that start out again, checking my clutch is ready for the British grand prix," said Warwick.

The fact the pendulum has swung in Rosberg's favour, particularly as Hamilton griped about his clutch, has raised suggestions it is Mercedes' German star who is better at systematically developing a car over a season.

Asked if he was key to the new clutch system, Rosberg said: "There are many things that I play a role in.

"But the decision to change was made by the team. It was about getting a better consistency in the starts with both cars," he told Kolner Express newspaper.

Asked about Hamilton's complaints about the system, Rosberg added: "I don't want to comment on that."

What he is happy to comment on, however, is his return to form, winning three of the last four grands prix and closing the championship gap to just 10 points.

"Of course it's a positive trend that I'm in," said Rosberg. "You could say that I feel back on the form of last summer."

Asked if he will be making Hamilton 'nervous' ahead of the Briton's home race this weekend, Rosberg answered: "That would be nice, but I concentrate more on my performance.

"I know we will have a top car. Two years ago I won at Silverstone and last year I retired in the lead with a broken gearbox. So it's a good place for me."